Radial velocities of AW UMA second component

The detection of the very faint profile of the secondary component in AW UMa leads to a new spectroscopic determination of the mass ratio, q_sp_=0.092+/-0.007, which is close to the previous, medium-resolution spectroscopic result of T. Pribulla & S. M. Rucinski, q_sp_=0.101+/-0.006, and remains substantially different from a cluster of generally accepted photometric results by several authors, concentrated around q_ph_=0.080+/-0.005.

A survey of binaries with the best-determined values of the mass ratio shows a common tendency for q_ph_<q_sp_. The tendency for systematically smaller values of q_ph_ may result from the overfilling of the primary lobe and underfilling of the secondary lobe relative to the Roche model geometry, as predicted by the K. Stepien model. Despite the observed moderate inter-systemic velocities, the photometric Lucy model may remain useful in providing approximate, though biased, results for the mass ratio.